Blood glucose monitoring system
A method and apparatus for blood glucose monitoring is provided which allows blood sampling and insulin infusion through the same catheter lumen of a multi-lumen, central venous catheter. It is designed to be used with a nearby continuous glucose sensor. The catheter lumen with the most proximal aperture leads to a connecting tube which is split into two parts, with both parts having a low internal volume. The described catheter allows for rapid switching between insulin delivery and blood sampling and minimizes the amount of purge fluid needed to clear the line.
A landmark study by Van den Berghe and colleagues, published in the Nov. 8, 2001 issue of the New England Journal of Medicine, showed improved outcomes in critically ill patients when blood glucose levels were kept in the normal range. Due to the release of stress hormones in very sick patients, or following major surgery or trauma, there is a natural tendency toward elevated blood sugars. Preventing hyperglycemia, without inadvertently causing hypoglycemia, is now the common goal in all hospital ICUs in the developed world.
An IV insulin infusion, most often given through one lumen of a central venous catheter, is universally used to suppress elevated blood sugar when it occurs, and the rate of infusion is judged from blood sugar measurements. Finger stick blood samples on an hourly basis and the use of a handheld glucometer is presently the most common method of tracking patient blood sugar levels. A system that could test blood sugar automatically without finger sticks would be a major improvement in the care of the critically ill. Besides avoiding the pain of finger sticks, it would give a more accurate picture of blood sugar levels by testing at least once every 10 minutes. Hourly tests are simply too infrequent to discern sudden rises or falls of blood glucose, which should be quickly adjusted for by changing the rate of the insulin infusion. Additionally, an automated system would save at least 40 minutes of a caregiver's time in a typical 8-hour nursing shift. Finally, there could be no contamination of personnel or equipment if finger stick samples were avoided.
In contrast to the prior art system of
It would be much preferred by the medical staff of a typical hospital that a single lumen of the catheter be used for both the withdrawal of blood samples for testing and for the infusion of insulin to control blood sugar, leaving the other lumens available for other IV fluids. The present invention fulfills this preference of ICU caregivers.
Regardless of sensor location, in any system of blood withdrawal and return, a column of fluid in the sampling line is in continuity with the blood inside the venous catheter. Reversal of the peristaltic pumps (items 41 or 42 of
An inherent problem in attempting to utilize a single lumen for blood sample withdrawal and insulin infusion is that serious complications for the patient may occur with an interruption of insulin infusion for an extended period of time. It is absolutely critical to limit the time period or “cycle time” of the blood withdrawal, testing and return of the sample to the patient. The present invention achieves these goals as discussed below.
In most present day ICUs, one lumen of a triple lumen catheter is used for the patient's insulin infusion, leaving two lumens for other purposes. Ideally, an insulin infusion pump infuses fluid at a steady rate without peaks or valleys in the delivery of fluid to the patient. A typical infusion rate of a fluid with insulin is 3 mL/hr, but the rate can vary between 1 and 6 mL/hr depending on patient blood sugar levels. If a standard central venous catheter were to be used for both the insulin infusion and the withdrawal of blood samples, a time delay in insulin delivery would follow the return of each blood sample. This is because of the relatively large fluid capacity of typical catheters and specifically in their connecting tubes. It can be shown that if a standard catheter were to be used for both sampling and the infusion of insulin, at a rate of 3 mL/hr. between 8 and 10 minutes would elapse before insulin would appear at the aperture of the catheter after return of a test sample. When a new sample is taken during the cycle and then returned to the patient, all the insulin which has accumulated in the connecting tube is delivered to the patient as a bolus, along with the returned blood sample. A drop in blood sugar is likely from a sudden infusion of a large amount of insulin, which is undesirable. By contrast, the short period (2.5 minutes or less) of non-insulin infusion, when using the device of the present invention (
The present invention changes to some extent the design of the present day triple lumen catheters. It should be noted, however, that these changes are only to the connecting tubes (the “tails”) of the catheter and not to any feature inside of or pertaining to the inserted part of the catheter. A patent granted to Martin (U.S. Pat. No. 6,206,849) and a recent application by Markower (U.S. 2007/0208252) claim various new catheter features. These features involve only that part of the catheter that is inserted under the skin of the patient. Nowhere do either Markower or Martin show in the figures or describe in their patent texts any changes in the connecting tubing leading up to the inserted portions of the catheter. The Markower and Martin patents are concerned only with the design of those parts of the catheter under the patient's skin. For example, in column 5, lines 48-50 of the Martin patent, it is stated that “this lumen (best seen in
A primary object of the invention is to provide a blood glucose monitoring system wherein only one lumen of a central venous multi-lumen catheter is used for both the blood sampling and for the infusion of insulin.
A further object of the invention is to alternate easily between blood sampling and insulin delivery.
A further object is to cause a minimal time delay in the delivery of insulin into the patient's central vein in order to withdraw, test and return a blood sample.
A further object is to minimize the infusion of additional purge fluid to clear the system after blood sampling.
A further object is to introduce modifications to a standard catheter without increasing the cost of manufacture.
As noted above, the present invention (shown best in
The data of
A first Y-shaped connecting tubing 375 has a stem end 376, a first arm 377, a second arm 378, with the stem end 376 in fluid communication with, and extending outwardly from, the body 325 of catheter 300.
The first arm 377 of first connecting tubing 375 is connected to testing unit 316 through a luer fitting 383, forming a fluid connection between the stem end 376 and testing unit 316.
The second arm 378 of first connecting tubing 375 is connected through tubing 385 to a source 399 of insulin infusion fluid, forming a fluid connection between stem end 376 and the source 399 (shown schematically) of insulin infusion fluid.
The multi-lumen catheter 300 has a second connecting tubing 332 extending outwardly from body 325 to form a fluid connection with a source 398 (shown schematically) of one other fluid (such as blood, antibiotics, etc.) to be infused into the patient through a different lumen of catheter 300. A third connecting tubing 333 extends outwardly from body 325 and is connected to a third source (not shown) of infusion fluid.
As shown by
The patient shown in
The invention also includes the method of providing a first passageway (i.e. stem 376 and first arm 377) extending from catheter body 325 to testing unit 316, wherein the passageway has an internal volume of 0.1 mL or less and preferably 0.02 mL or less.
The method also includes providing a second fluid passageway (i.e. stem 376 and arm 378) that intersects with and in fluid communication with the first fluid passageway by being in fluid communication with stem 376. The second fluid passageway is connected (by tubing 385) to a continuous source 399 of insulin solution. The second fluid passageway also has a combined internal volume (i.e. of stem 376 and second arm 378) of 0.1 mL or less and preferably 0.02 mL or less.
The method includes the further step of periodically actuating the reversible peristaltic pump (41 or 42 of
The method also includes the step of continuously infusing insulin through the second passageway through the same one lumen of catheter inserted part 350 used to withdraw blood samples, wherein the combined internal volume of the second passageway (i.e. stem 376 and arm 378) is 0.1 mL or less and preferably 0.02 mL or less.
The method also includes the step of interrupting the continuous infusion of insulin for less than 3.0 minutes and preferably less than 1.8 minutes to withdraw, test and return the blood sample to the patient.
The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teaching. The embodiments were chosen and described to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best use the invention in various embodiments and with various modifications suited to the particular use contemplated. The scope of the invention is to be defined by the following claims.
Claims
1. In an apparatus for automatically and periodically sampling and testing blood glucose from blood samples withdrawn through an intravascular multi-lumen catheter inserted into the subclavian or other central vein of a patient, wherein a small testing unit is in fluid communication with said catheter, wherein said testing unit is cleared of blood after each test with a known purge volume of purging fluid, wherein a bedside monitor has at least one reversible peristaltic pump for either pumping blood samples outwardly from said patient into said testing unit, or pumping said blood samples from said testing unit inwardly and back into said patient through said catheter, the improvement comprising:
- said intravascular multi-lumen catheter having a body and having a first part that is insertable into the subclavian or other central vein of said patient,
- said multi-lumen catheter having a first Y-shaped connecting tubing having a stem end, a first arm and a second arm, with said stem end being in fluid communication with, and extending outwardly from said body,
- said first arm being connected to said testing unit and forming a fluid connection between said stem end and said testing unit,
- said second arm being connected to a source of insulin infusion fluid and forming a fluid connection between said stem end and said source of insulin infusion fluid,
- said multi-lumen catheter having at least a second connecting tubing that extends outwardly from said body to form a fluid connection with a source of one other fluid to be infused into said patient through said intravascular catheter,
- said stem and said first arm of said first Y-shaped connecting tubing having a combined internal volume of 0.1 mL or less,
- wherein insulin is continuously infused through said stem of said first connecting tubing into said patient, except when blood samples are being withdrawn from said patient through said stem and said first arm of said first connecting tubing and then tested.
2. In the apparatus of claim 1, wherein each glucose testing cycle, including withdrawal of a blood sample, testing and purging are all completed in 3.0 minutes or less.
3. In the apparatus of claim 1, wherein both said stem and said first arm and said stem and said second arm of said first connecting tubing each have a combined internal volume of 0.02 mL or less.
4. In the apparatus of claim 3, wherein each glucose testing cycle, including withdrawal of a blood sample, testing and purging are all completed in less than 1.8 minutes.
5. A method for continuously infusing insulin solution through, and for periodically withdrawing and testing blood samples from, one lumen of a multi-lumen intravascular catheter connected to the subclavian or other central vein of a patient, wherein a small testing unit is worn by the patient near the body of said catheter, wherein the testing unit is cleared of blood after each test with a known volume of purge fluid, wherein a bedside monitor has at least one reversible peristaltic pump for either pumping blood samples outwardly from said catheter into said testing unit or pumping said blood samples from said testing unit inwardly and back into said patient through said catheter, and wherein a source of insulin solution is provided, comprising the steps:
- providing a first fluid passageway extending from said catheter body to said testing unit, wherein said first fluid passageway has a volume of 0.1 mL or less,
- providing a second fluid passageway that intersects with and in fluid communication with said first fluid passageway, and wherein said second fluid passageway is connected to said continuous source of insulin solution,
- periodically actuating said reversible peristaltic pump to withdraw a blood sample through said one lumen of said multi-lumen catheter and through said first passageway into said testing unit,
- testing said withdrawn blood sample in said testing unit,
- pumping said blood sample from testing unit along with a known volume of purge fluid through said first passageway and said one lumen back into said patient,
- continuously infusing insulin solution through said second passageway and through said one lumen of said multi-lumen catheter into said patient wherein said second passageway has an internal volume of 0.1 mL or less,
- interrupting said continuous infusion of insulin for 3.0 minutes or less to withdraw, test and return said blood sample to said patient.
6. The method of claim 5 wherein each of said first and second fluid passageways extending from said catheter body has an internal fluid volume of 0.02 mL or less.
7. The method of claim 6, wherein said interruption of said infusion of less is less than 1.8 minutes to withdraw, test and return said blood sample to said patient.
Type: Application
Filed: Jan 25, 2010
Publication Date: Jul 28, 2011
Inventor: Paul D. Levin (Santa Cruz, CA)
Application Number: 12/657,639
International Classification: A61B 5/145 (20060101); A61M 5/14 (20060101);